Let us discuss it fully to clear doubts. I am sharing what I know at present as follows -
1. Title of a forum thread can be edited. However once a thread is submitted, an url is assigned to the thread by the system which contains the title also besides a serial number e.g. in the present thread the url is -'http://www.indiastudychannel.com/forum/146759-Title-can-not-be-edited.aspx'.
After editing the title of this thread, the url will remain the same containg the 'Title-can-not-be-edited.aspx' component.
There had been cases in the past when unknowing authors had totally transformed the title as well as the body of the thread, though url remained the same containing the original title.
2. Same is the case with articles also. On submission, the system generated url will contain the serial number as well as the selected title. On editing, new title will appear in the article though in the url, only original title will appear.
Let us encourage each other in sharing knowledge.